Fixed bridge prosthetic replacements for missing teeth and splinted prostheses are generally well known in the art of dentistry and in widespread use. In a typical fixed bridge, one or more abutment supporting teeth located on either side of the span of missing teeth are used to suspend a row of false teeth, referred to as pontics, in a manner that cements or bonds the false teeth to the enamel of naturally occurring teeth so that the wearer cannot remove the structure (i.e., it is fixed in place). A fixed bridge design having abutment-supporting teeth on only one side of the span of missing teeth is referred to as a cantilever fixed bridge. A fixed splint connects two or more adjacent teeth to provide a brace for weakly supporting members of the combined structure and is used to reduce or prevent mobility of weakly supported teeth. A fixed splint does not necessarily contain pontic replacements of missing teeth but is cemented or bonded in a manner similar to fixed bridges.
Previously, conventional fixed bridges were accomplished by the attachment of crowns, inlays, onlays or a combination of these structures with suitable cement to the prepared (or shaped) abutment-supporting teeth. The shaped abutment-supporting teeth were then reproduced in form and position for a waxed facsimile to be cast by means of the lost wax process with the completed fixed bridge containing the abutment restorations, pontics, and any veneer or covering for increased aesthetics. The pontic replacements are attached to the abutment restorations via unit casting or by soldering. This process, from start to finish, requires a high degree of dental and technical custom fabrication skill, many patient appointments, removal of significant portions of tooth structure that may be otherwise sound, accurate impression technique and materials, a temporary fixed bridge to keep the shaped abutment-supporting teeth in a stable position, and is costly. Consequently, much of the progress in fixed bridge construction has focused upon reducing many of these disadvantages of the conventional fixed bridge while, at the same time, reducing the cost.
With increased use of bonded resins and new technology in etched metal fabrication, bonded resin metal-based fixed bridges became possible. These structures, referred to collectively as Maryland-type bridges, bond metal connectors externally to the enamel of abutment-supporting teeth. The fixed placement of the bridge, however, is totally dependent upon the bonding vehicle. The metal connectors must cover a significant width and more than half the circumference of the abutment tooth enamel in addition to an occlusal rest seat for adequate bonding to prevent displacement. The large amount of visible metal makes this type of bridge non-aesthetic and frankly unsightly. Moreover, the bonding technique is highly sensitive to moisture, which results in a weakened bond. The structure is susceptible to forces causing torque and, therefore, is contraindicated in cantilever fixed bridge designs and where some of the abutment-supporting teeth are mobile. Bonding strength to the external surfaces of the enamel is seriously jeopardized by inherently weak and poorly mineralized enamel. Failure of the structure to remain fixed is a direct result of the failure of the bond to the external surfaces of the enamel. The Maryland-type bridge, moreover, is a custom fabrication process accomplished in a dental prosthetics laboratory.
More recently, a fixed bridge composed almost exclusively of bonded resin is proposed under the trade name "California Bridge", of Kulzer Laboratory, Inc. of Irvine, Calif. The resin fixed bridge abrades down more easily against natural dentition and against porcelain-covered opposing teeth than do porcelain restorations. Moreover, it requires that the teeth be prepared for the restoration, an impression made of the prepared sites, and temporary fillings placed between patient appointments. A thin nondescript metal substructure may be used solely to support the pontic. The resin fixed bridge is inherently weak, particularly over longer pontic spans. In principle, this bridge is no different than a conventional fixed bridge except that the dental material used for the California fixed bridge design is made of resin compatible with current bonding techniques.
Fixed splints that make use of castings, model construction or indirect fabrication restorations utilize techniques and materials similar to fixed bridges. The splint restoration is cast as one piece or soldered into a single unit having no pontic and cemented to adjacent natural teeth to lock them together.
More direct in-mouth techniques exist to rigidly hold teeth that are otherwise loose or mobile. All of the direct techniques are variations of materials for the purpose of splinting teeth. Stainless steel wire may be used to wrap around the exteriors of both loose teeth and the more stable teeth to which they are splinted; the wire may then be covered or attached with acrylic or resin. This technique of ligation is commonly practiced. Other materials are used for splints without the need to wrap the affected teeth. A mesh of stainless steel, titanium, silk or other material adapted to the lingual surfaces of anterior teeth and covered with resin has been used. Notched or perforated metal bars of either stainless steel or other suitable metal alloys have been used for the purpose of splinting teeth. In this technique, long grooves are cut across the occlusal surfaces of adjacent teeth, the bar placed at the base of the groove preparation, and the groove filled with resin to lock mobile teeth to more stable adjacent teeth. One such splinting bar resembling a miniature I-beam, referred to as "Titanium Splinting Bar", commercially available from Zeza (Davie, Fla.), is used for immediate space maintenance, splinting for periodontally loose teeth and repair of broken solder joints of prosthetic appliances.
The replacement of missing teeth may also be accomplished with the use of a removable prosthesis, sometimes referred to as a "partial denture". The removable partial denture is indicated where the arrangement and/or the supporting strength of the remaining teeth in the oral cavity cannot support a fixed bridge. Removable partial dentures are comparatively less expensive than fixed prostheses and can be used when cost to the patient is an overriding factor. The position of the removable partial prosthesis is stabilized in the oral cavity by a system of connectors to the abutment natural teeth.
The connectors clamp externally around the abutment-supporting teeth and are called clasps. This type of clamping mechanism around natural teeth is both unpleasant in its appearance and a significant accumulator of bacterial plaque, causing tooth decay against the surfaces of the teeth needed to support the stability of the removable partial denture.
Connectors are also fabricated with interlocking members so that one member is cast into a newly constructed crown with the corresponding member attached to the partial denture. The designs of the interlocking members are numerous but each requires that a crown be fabricated which is costly, requires high dental proficiency, removes unnecessary tooth structure and is time consuming. Additionally, the interlocking components of the partial and the crown wear against one another rapidly and are not readily repairable except with fabrication of a new appliance.
There is thus a need to develop fixed bridges, splints and removable prosthesis attachments having a simplified construction that eliminates the need for customized bridge construction, simplifies dental chairside procedures, reduces destruction of sound tooth structure and generally lowers cost.